In the drilling and completion of oil wells, it is common to drill a section of borehole to a desired depth and then cement a liner or casing in the borehole. The liner or casing to be cemented in the bore carries with it conventional cementing equipment such as a cementing shoe, collar and valves. When the casing or liner is properly positioned in the borehole, a cement slurry is pumped through the casing or liner displacing mud and is passed from the casing shoe into the annulus between the casing or liner and the borehole. The cement slurry is moved upwardly in the annulus to the desired level and the cement slurry is permitted to set or cure. When the cement has set it is intended to provide load supporting strength for the casing or liner as well as provide a fluid seal with respect to the interfaces between the cement and borehole well and between the cement and the pipe or casing. For various reasons, it is not always possible to obtain a good bond between the outer surface of the casing or liner and the column of cement.
To enhance the bonding of cement to the casing it has heretofore been proposed to coat the outside of the liner or casing (sometimes referred to as "pipe") with a layer of material having a rough surface. The rough surface material is formed by bonding solid grit-like particles (sand, metal or the like) to the mandrel surface by a suitable binder such as an epoxy resin. The rough surface of the epoxy impregnated bonding material provides for increased roughness and particles on the surface of the pipe therefore improves the bonding relationship of the cement relative to the pipe. However, the addition of the epoxy and grit-like material to the pipe affects the acoustical transmission properties of the pipe. Thus, when a pipe is cemented in the borehole and a cement bond logging or log (CBL) tool is run through the pipe to obtain a cement bond log, it has been found that the amplitude of the sonic signal on the CBL log obtained by the CBL tool is increased which typically indicates a lack of bonding of cement at the interfaces between the cement and the borehole or pipe. This increase in amplitude, however, is an erroneous representation because the amplitide of the sonic signal is affected by the epoxy and grit-like material. Therefore, a customer has an uncertainty about the bonding of the cement at the interfaces along the pipe.
The present invention involves the use of a specially prepared pipe for lining a borehole in which the advantages of the epoxy rough coating are retained and the adverse effects of the epoxy rough coating to the logs obtained by a CBL tool are eliminated.